Railway signaling apparatus



Oct. 1, 1940. B. E. O'HAGAN RAILWAY SIGNALIYG- APPARATUS Filed Jm 28;1939 ATTORNEY Patented Oct. 1, 1940 UNITED STATES RAILWAY SIGNALINGAPPARATUS Bernard E. OHagan, Swissvale, Pa, assignor to The Union Switch& Signal Company, Swissvale, Pa., a corporation of PennsylvaniaApplication June 28, 1939, Serial No. 281,556

Claims.

My invention relates to railway signaling apparatus, and has particularreference to apparatus of the type employed in rail-way signalingsystems in which coded trackway energy is utilized to control either orboth wayside signals and train carried cab signals.

The code responsive apparatus heretofore proposed for use in railwaysignaling systems of the above described class usually requires that anappreciable amount of energy be supplied to the apparatus from the trackrails of the section to effect proper operation of such apparatus. Suchsystems accordingly require that a relatively large amount of trackwayenergy be supplied the rails of a section in order to obtain the properenergy level across the track rails necessary to properly operate theassociated code responsive apparatus. An object of my present inventionis the provision of novel and improved code responsive apparatus whichis highly sensitive to relatively small amounts of trackway energy,whereby more efiicient operation of the code responsive apparatus iseffected by supplying the track rails of a section with relatively smallamounts of trackway energy, thereby reducing the power requirementnecessary to effect operation of the code responsive apparatus;

Another object is to provide sensitive code responsive apparatus havingno moving parts, and which is capable of followingmuch higher code ratesthan is possible with code following apparatus having moving mechanicalmembers.

A further object is to provide novel and improved coderesponsiveapparatus having no moving parts, which reproduces codedenergy without distortion of the characteristics of the control code.

An. additional object is the provision of novel and improved cut sectionfacilities 'to cascade trackway energy from one subsection to the next,and which apparatus is responsive to relatively small amounts oftrackway energy.

A further object is to provide novel and improved means for controllinga saturation type relay to cause coded energy to be supplied from thesaturation relay without distortion of the reproduced coded energy.

Other objects and advantages of my invention will appear as thedescription progresses.

I shall describe one form of apparatus ernbodying my invention, andshall then point out the novel features thereof in claims.

The accompanying drawing is a diagrammatic view of a preferred form ofapparatus embodying my invention.

Referring to the drawing, the reference characters l and la designatethe track rails of a stretch of railway track over which traflicnormally moves in the single direction indicated in the drawing by anarrow, and which I shall as- 5 sume to be the westbound direction. Thetrack rails of the stretch are divided by means of the usual insulatedrail joints 2into a plurality of successive adjoining track sections, ofwhich only one section, 3-4, is shown complete in the drawing. Section 3l further is divided into a plurality of adjoining subsections, whichare formed by interposing insulated joints 2- in the rails of section3--4 at so-called cut section locations, and as shown, section 3,4 isdivided by joints .2 located at out section location 30. into an advancesubsection 3-30, and a rear subsection Each track section is providedwith a signal, designated by the reference character S with a .20distinguishing suffix, located adjacent the entrance end of the sectionfor governing traffic operating thereover. Signals S may take any one ofseveral suitable forms but in the form herein shown are three-indicationsignals of the color light type, and each signalcomprises a red lamp R,a yellow lamp Y and a green lamp G, which lamps when illuminatedindicate stop, approach and clear, respectively.

Each section is further provided with means, located at the exit end ofthe section, for supplying to the rails of the associated section codedtrackway energy, the code frequency or rate of which is controlled bytraflic conditions in 1 advance. Thesemeans areherein shown in the usualform and comprise a track transformer, designated by the referencecharacter TT with a distinguishing suffix, the secondary winding ofwhichis constantly connected with the rails' 'of the associated section inseries with the usual 24 current limiting impedance 5. The primarywinding of transformer'TT is connected with the terminals BX and CK of asuitable source of alternating current (such as a generator not shown inthe drawing) over one contact I or over 45 another contact of a codingdevice, designated by the reference character CT plus a distinguishingsufi'ix, according as a front contact 6- 611 or a back contact 6-617 ofa relay, designated by the reference character H with a. distinguishing:5

sufiix andwhich is associated with the section neXt in advance, isclosed. Each codingdevice CT is constantly supplied with current from .asuitable source of current, the terminals ofwhich .are indicated by thereference characters .BX .55

and OK and each device periodically opens and closes its contact 80 atthe rate of 180 times per minute, and also opens and closes its contactT5 at the rate of 75 times per minute. It is readily apparent,therefore, that when the relay H of a section is picked up so that itsfront contact t6a is closed, the rails of the section next in the rearare supplied with alternating trackway energy which is periodicallyinter rupted or coded at the rate of 180 times per minute, but that,when the relay H of a section is released so that its back contact 6tbis closed, the rails of the section next in the rear then is suppliedwith alternating trackway energy which is periodically interrupted orcoded at the rate of '75 times per minute; The 180 code is used toprovide a clear indication and the 75 code is used to provide anapproach indication for the signal of the associated section, in amanner which will be made clear as the description proceeds. Each relayH is controlled by trafiic conditions in the associated section in amanner which also will be made clear as the description proceeds. It isto be understood, of course, that while only the apparatus (whichcomprises coding device GT4 and relay H4) which controls the supply ofenergy to the primary winding of track transformer TT l is shown in thedrawing, similar apparatus is provided to control the supply of energyto the primary winding of track transformer TTS, this latter apparatusbeing omitted from the drawing since it would be but a duplication ofthe apparatus shown associated with track transformer TT i.

Section 3--4 also is provided with cut section facilities for cascadingtrackway energy from one subsection into the next. The cut sectionfacilities shown in the drawing positioned at the cut section location311 of section 3-4, includes an electronic tube, designated by thereference character Tl, controlled by the trackway energy of the advancesubsection for supplying the rails of the rear subsection with trackwayenergy coded at a rate corresponding to the code rate of the trackwayenergy of the advance subsection.

The electronic tube TI as shown comprises two spaced electrodes, ananode or plate I and an electrically heated cathode or filament 8, and acontrol grid 9. Heating current for the cathode is supplied from aportion of secondary Winding H] of a transformer PTI, which transformerhas its primary winding H connected across the source of alternatingcurrent designated by the reference characters BX and CK. The above tubeelements are enclosed in a sealed envelope, and preferably this envelopeis filled with a medium, such as neon gas, which forms a conducting pathbetween the two tube electrodes when and only when the potential betweenthe electrodes exceeds a value which depends upon the relative potentialof the grid with respect to one of these electrodes. As the descriptionproceeds, however, it will be apparent that tube Tl may be of any othertype which is adapted to pass current when a suitable potential isapplied to its grid, and which is adapted to remain non-conducting atall other times.

The particular type of the tube shown, however, is characterized by thefact that for a given plate potential, the tube is rendered conductingonly when its anode is positivewith respect to its cathode; and furtherthat once the relative potential of the grid and the cathode is suchthat the medium has formed its conducting path, the tube remainsconducting irrespective of the grid potential until such time as theplate potential is removed or reversed, and in which latter event thetube becomes non-conducting and remains so until the anode is againpositive with respect to the cathode and the proper grid potential isapplied to break down the tube medium.

The tube Ti is arranged with its two electrodes forming a part of acircuit which includes secondary winding iii of transformer PTl, and thepotential which transformer PTi normally impresses across the twoelectrodes is chosen to be somewhat less than the critical or breakdownvalue under conditions of a predetermined negative grid potential.Negative grid potential nor mally is established on the tube by means ofa resistor l4 and a rectifier i2, and which rectifier has its inputterminals connected across another secondary winding I3 of transformerPTi. The positive output terminal of rectifier i2 is connected to oneterminal of grid resistor it and also to filament 8 of tube Ti, and thenegative output terminal of rectifier i2 is connected to grid resistorHi through the medium of an adjustable contact finger l5, the otherterminal of resistor it being connected with grid 9 of the tube. Theresistance across the output terminals of rectifier I2 is adjusted bymeans of contact finger E5 to cause rectifier I2 to apply thepredetermined negative grid potential to tube TI, with the result thattube Tl normally is non-conducting. If, however, there is applied to thegrid in opposition to the negative biasing potential of rectifier l2 asdetermined by the position of contact l5 on resistor M, a controlpotential having the proper magnitude and phase relation, the relativepotential of the grid with respect to the cathode is then made such thatthe critical breakdown potential of the tube under these conditions isless than the potential impressed across the anode and cathode of thetube by secondary winding it of transformer PTl, and as a result themedium of the tube breaks down to render the tube conducting. By virtureof the fact that secondary winding ll! of transformer PTl supplies theplate circuit of the tube TI with alternating current, the relativepolarity of the anode and cathode of the tube is reversed twice duringeach cycle, and as a result rectified current having half wave form ispermitted to flow in the plate circuit each time that the anode ispositive with respect to the cathode, provided that the grid voltage issuch as to make the tube conducting. The alternation of potential of theplate circuit, therefore, renders the tube self-restoring when the gridcontrol potential is removed, since the interruption and reversal of theplate potential will restore the tube to its non-conducting conditionupon the negative biasing grid potential again becoming effective.

The above-mentioned control grid potential is applied to the tube Tlfrom a rectifier l5 receiving energy from the track rails of advancesubsection 3-3a through the medium of a receiving transformer RTSa,which transformer has its primary winding connected across the trackrails of subsection 33a and has its secondary winding connected to theinput terminals of rectifier [6. The positive output terminal ofrectifier I6 is connected to grid 9 of tube TE, and the negative outputterminal of the rectifier is. connected to cathode 8 of tube Tl over acircuit which in cludes contact finger l5 and a portion of grid resistorM. It is apparent, therefore, that rectifier l6 applies across the gridand cathode of tube Tl a positive grid potential which opposes thenegative biasing grid'potential f rectifier [2. The electromotive forcesof rectifiers. l2 and I6 are so proportioned'and designed'that wheneverboth rectifierS are supplying energy to the grid circuit of tube TI, theresultant electromotive force is sufficient to cause the tube medium tobreak down and become conducting in response United States Letters tothe plate circuit potential established .by winding ll? of transformerPTI.

Trackway energy is supplied to the rails of subsection 3a4 through themedium of a track transformer TT3a, which has its secondary windingconstantly connected across the rails of be connected directly acrossthe electrodes of tube T! in series with secondary winding 10 oftransformer PTI, and under these conditions, the rectified current ofhalf wave form passed by tube- Tl during its conducting period-will besuppliedto transformer TT3a and as a result the track rails of the rearsubsection will be supplied with trackway energy having alternatingcurrent characteristics and also a code rate corresponding tothe coderate of the trackway energy supplied to the rails of the advancesubsection. However, it is preferredthat tube Tl control means forsupplying the transformer TT3a with alternating current. In theparticular embodiment of my invention shown in the drawing, theparticular means chosen to supply transformer TT3a with alternatingcurrent is a saturation relay, designated by the reference character DR.

Saturation relay DR may be of any suitable type, but as here shown is ofthe type shown in Patent No. 1,936,705 granted to H. D. Abernethy onNovember 28, 1933. This relay comprises a three-legged magnetizable corel1 having a control winding l8 mounted on the middle leg of the core andconnected in series with secondary winding H) of transformer PTI over acircuit which includesthe anode i and, cathode 8 of tube TI. The relayfurther comprises two main or impedance windings l9 and 20 connected inseries and disposed one on each of the two outer legs of the core, thewindings I9 and 20 being connected in series and so arranged that whensupplied with alternating current, the windings send flux in oppositedirections through the middle leg of the core so that no .current willbe induced in control winding l8. The main windings of the relay DR areconnected across the source of alternating current in series with theprimary winding of transformer TT3a. If now, control winding I8 of relayDR is deenergized, as, for example, during the non-conducting period ofthe tube Tl, the main windings l9 and 20 of the relay represent a highimpedance in series with the primary winding of transformer TT3a so thatthis transformer receives practically no energy. When, however, controlwinding I8 is supplied with energy during the conducting period of thetube Tl, the rectified current flowing in winding [8 supplies aunidirectional flux to the relay core which varies the permeability ofthe core'to the alternating flux created by windings l9 and 29, and asa'result the impedance of windings l9 and 2|] is decreased andalternating current is permitted to flow in the primary winding oftransformer TT3a. Transformer TT3a, therefore, will be energized duringthe interval and for'the. period: tube .TI is .con-

energy of subsection 3-3a is coded. The trackway energy of subsection3-3a is therefore cascaded around cut section location 3a of section 3-4from the advance subsection into the rear subsection.

'An advantage of the cut section facilitates embodying my invention anddescribed above is that such apparatus is higly sensitive; requires buta relatively small amount of trackway current for operation; andprevents distortion of the trackway energy supplied to the rearsubsection in that the opening of the circuit for the control winding ofthe saturation relay due to the restoration of the tube to itsnon-conducting condition during the off period of the code, causes avery rapid decay of the saturating flux in the relay core whereby asharp cut off is effected in the energy supplied to the tracktransformer TI'lla. and to the rear subsection.

Each section also is provided with code following and decoding apparatuspositioned adjacent the entrance end of the section to controlthe'associated wayside signal and the supply of trackway energy to thesection next in the rear. The code following and decoding apparatusshown in the drawing located at signal location 4 comprises two tubes T2and T3 (which preferably are similar to tube Tl hereinbefore described)controlled by energy derived from subsection 3a4 and supplying energytoa decoding transformer DT from a source of alternating current hereshown as a transformer PT2. Transformer PTZ has its primary winding 2|connected to the terminals BX and CK of the source of alternatingcurrent, and a portion of its secondary winding 22 constantly suppliesheating energy to the cathodes 8 of tubes T2 and T3. The left-handportion (as viewed in the drawing) of secondary winding" 22 oftransformer PT2 is connected across the electrodes 1 and 8 of tube T2over a plate circuit which includes primary winding 23 of decodingtransformer DT. A four-lead condenser 24 also is connected across theprimary winding 23 of transformer DT for a purpose later to beexplained, and has its plates connected in series in the plate circuitof tube T2 on opposite sides of winding 23'. The righthand portion ofsecondary winding 22 of transformer PTZ is connected across the twoelectrodes 1 and 8 of tube T3 over a plate circuit which includesanother primary winding 25 of decoding transformer U1, and this primarywinding25 also has a condenser 26 connected across its terminals withthe plates of such condenser connected in series in the plate circuit oftube' I3. 7

Tube T2 normally is caused to be non-conducting by virtue of a negativegrid biasing potential which is applied over an obvious circuit acrossthe grid and filament of tube T2 by a resistor 38 and a biasingrectifier 21, which rectifier receives energy from a secondary winding28 of transformer PT2. Tube T3 normally is caused to be conducting byvirtue of a positive grid biasing potential which is applied over anobvious circuit across the grid and filament of tube T3 by a resistor 39and a biasing rectifier 29, which rectifier constantly receives energyfrom a secondary winding 3110f transformer PTZ. It is apparent,therefore, that with tube '12 normally non-conducting,

primary winding 23 of. decoding transformer DT is normally deenergized.Primary winding 25 of decoding transformer DT, however, normally isenergized by the rectified. half wave current passed by tube T2 (whichis normally conducting), which current sets up in primary winding 25 aunidirectional flux having a polarity indicated by an arrow in thedrawing.

A receiving transformer RT E also is provided for section 3-4 adjacentits entrance end 4, and which transformer has its primary windingconstantly connected across the rails of subsection 3a4. The secondarywinding of transformer RT4 is connected across the input terminals oftwo rectifiers 3i and 32 for supplying energy to such rectifiers fromthe rails of subsection 3a4. Rectifier 33 is connected across the grid 9and filament 8 of tube T2 over an obvious circuit including resistor 33in such manner as to apply a control potential, opposing the biasingpotential of rectifier 27, whereby when rectifier 3! is receiving energyfrom the rails of subsection 3a4, tube T2 is caused to becomeconducting. Tube T2 under the above condition, therefore, suppliesrectified half wave current to primary winding 23 of decodingtransformer DT, which current sets up in the winding a unidirectionalflux having a polarity indicated in the drawing by an arrow. Rectifier32 is connected across the grid 9 and cathode 8 of tube Til overanobvious circuit ineluding resistor 39 in such manner as to apply acontrol potential which opposes the biasing potential of rectifier 29,whereby when rectifier 32 is receiving energy from the rails ofsubsection 3a4, tube T3 then is caused to become nonconducting. Underthe above condition, therefore, primary winding 25 of transformer DTwill be deenergized. It can be seen from the foregoing that primarywinding 25 of decoding transformer DT is supplied with unidirectionalflux of one polarity when tube T3 is caused to be conducting during theinterval energy is not present in the track rails of subsection 3a--4(as for eX- ample during off periods of the coded trackway energysupplied to sections 34), and that primary winding 23 of decodingtransformer DT is supplied with unidirectional fiux of the otherpolarity when tube T2 is caused to be conducting during the intervalthat energy is present in the track rails of subsection 3a4 (as forexample during the on period of the coded trackway energy) It follows,therefore, that whenever coded trackway energy is received by thereceiving transformer from the rails of subsection 3a-4, the primarywindings 23 and 25 of transformer DT are alternately supplied withimpulses of rectified current, and that such impulses will have a coderate which depends upon the code rate of the trackway energy present inthe rails of section 3-4. The impulses of rectified current which aresupplied to the primary windings 23 and 25 by tubes T2 and T3 set upopposing fluxes in the core of the transformer whereby the transformeraction of alternating current of relatively low frequency equal to thecode rate is simulated.

The condensers 24 and 26 are connected across primary windings 23 and25, as the case may be,

of transformer DT to smooth out and prevent any transformer action ofthe pulsating or half wave current which comprises the code impulses ofcurrent supplied to the primary windings of the transformer. Thecondensers 24 and 25, therefore, prevent transformer action in the eventthat either tube T2 or tube T3 is controlled continuously to itsconducting condition, and permit transformer action only in the eventthat code impulses of current are supplied to the primary windings oftransformer DT by tubes T2 and T3 in response to the coded trackwayenergy received from subsection Saw-4.

Decoding transformer DT is provided with two secondary windings 33 and34, one for each of two signal control relays H4 and AJ4. Relay H4 iscontrolled by energy supplied from secondary winding 33 of transformerDT through the medium of a full wave rectifier 35, which converts thealternating current induced in winding 33 of transformer DT in responseto the impulses of rectified current supplied to the primary windings oftransformer DT, into unidirectional current which is supplied to relayH4. This relay is a slow-acting direct current relay proportioned tohave slow pick-up characteristics and caused to be slow releasing byvirtue of the short-circuiting action of rectifier 35 connected acrossits terminals, and is effectively energized and picked up whenever 75 or180 code is applied to decoding transformer DT. Relay H4, therefore,functions as a code detecting relay since it is picked up on either ofthe two code frequencies, but is not picked up whenever half wavecurrent is continuously supplied to one primary winding of transformerDT by one tube only, due to the previously described action ofcondensers 24 and 26 in dampening the transformer action of thisrectified or half wave current.

Relay AJ 4 is controlled by energy supplied from secondary winding 34 oftransformer DT, through the medium of a decoding unit DU-l 80. Thedetails of construction of this unit are not shown in the drawing, butthis unit usually comprises a rectifier and a reactor condenser tuningunit tuned to resonance at a frequency corresponding to the 180 code,whereby relay AJ4 is effectively energized and is picked up when andonly when impulses of 180 code are supplied to transformer DT. RelayAJ4, therefore, functions as a code selecting relay since it is pickedup on 180 code but is released on 75 code.

The code selecting relay AJ4 and the code detecting relay H4 cooperatesto selectively control the various aspects displayed by signal S4, inthe following manner: When relays H4 and AJ4 are both picked up, signalS4 is caused to display its clear indication over a circuit which may betraced from terminal B through front contact 35-355; of relay H4, frontcontact 36--36a of relay AM, and the filament of lamp G of signal S l toterminal C. When the code detecting relay H4 is picked up and the codeselecting relay AJ tis released, signal S 3 then is caused to displayits approach indication over a circuit passing from terminal B throughfront contact 3535a of relay H4, back contact 3636b of relay AJ4 and thefilament of lamp Y of signal S4 to terminal (3. When, however, bothrelays H4 and AJ4 are released, signal S4 then is caused to display itsstop indication over a circuit passing from terminal B through backcontact 35-35?) of relay Ed and the filament of lamp R of signal S toterminal C.

The above selective control of signal S4 is effected by relays H4 andAJ4 in the following manner: Section 34 will be supplied with 180 codeor 75 code according as the section next in advance is unoccupied oroccupied. When section 34 is supplied with 180 code and the section isunoccupied, all parts of the apparatus will occupy the position in whichthey are shown in Fig. 1. Under the above condition, relays H4 and AJ 4are both picked up, the circuit for lamp G of signal S4 is completedwhereby that signal is caused to display its clear indication, and thecircuit including front'icontact 6J$a;:of relay H4 and contact I 80 ofadding device C'Id'is closed so that the section next in therear ofsection 34 is supplied with the 180 code also.

When section 3-4 is supplied with. 75 code and the section isunoccupied, relay H4 is picked up but relay AM is released, thus causingsignal 56 to display its approach indication since the circuitpreviously traced for lamp Y of signal S4 is now completed. The rails ofthe section next in the rear of the section 34, however, are stillsupplied with 180 code since front contact 6-6a of relay H4 is closed.

Whenever section 3-4 is occupied by a train, the coded trackway energysupplied to section 3@ then is shunted away from the code followingapparatus of that section. For example, whenever a train occupies rearsubsection Lia-4, the wheels and axles ofthe train then shunt thetrackway energy away from receiving transformer RTfi so that tub-e T2 iscontrolled constantly to its non-conducting condition and tube T3 iscontrolled constantly to its conducting condition. Under the aboveconditiomwinding of decoding relay DT is constantly supplied withrectified current of half wave for, but as was pointed out heretofore,no transformer action is effected by this current so that both relays AMand H4 are released and signal S4is controlled to its stop indicationover back contact -352; of relay 1-14. In like manner, when subsection3-3a is occupied by the train, the trackway energy is shunted away fromreceiving transformer RT3a and as a result tube T! of the cut sectionapparatus is constantly controlled to its non-conducting condition. Withtube Tl in its non-conducting condition, saturation relay DR iscontrolled to limit the energy supplied to track transformer TT3a and tothe rails of subsection Sat-4 to a relatively low value insufiicient toeffect the control of tubes T2 and T3 of the code following apparatus,and tube T3 is controlled by virtue of biasing rectifier 29' to itsconducting condition to constantly energize winding 25 of decodingtransformer DT with rectified half wave current. Since no transformeraction is effected by'this half wave current (due to the action of condenser 25), relays AJtand H4 are both released, andsignal S4 iscontrolled to-its stop indication, It is readily apparent from-the foregoing, therefore, that the coded trackway energy is shunted away fromthe code following apparatus of the section whenever a train occupieseither or both of the subsections comprising that I section, and thatthe two subsections when taken together cooperate to provide a singletrack section which is responsive to traffic conditions in the sectionin the same manner as if the rails of The code responsive apparatusaccordingly is capable of following much higher code rates than ispossible with code responsive apparatus having moving mechanicalmembers, since there is no inertia of the mechanical members to becontended with. Improved operation and efficiency of the decodingapparatus is effected by virtue of the sharp cut off in energy passed byweaee- I tronic tubes employed, whereby impulses are. supplied to thedecoding transformer having the same code characteristics as possessedby the coded trackway energy supplied tothe track rails of theassociated section. Furthermore, the control of the electronic tubesemployed is established by virtue of the potentials applied to thecontrol grids of the tubes, thereby requiring relatively small amountsof trackway energy for controlling the code responsive apparatus.

An, additional advantage is obtained by employing an electronic tubeinconnection with the cut section facilities which cascades trackwayenergy from the advance subsection to the adjoining rear subsection, inthat the trackway energy supplied to the rear subsection hassubstantially the same code characteristics as possessed by the trackwayenergy of the advance subsection, since a sharp cut off iseffected inthe high magnitude energy supplied through the saturation relay to therear subsection due to the fact that the saturating fiux of thesaturation relay decays very rapidly upon interruption of the flow ofenergy through tube Tl.

Although I'have herein shown and described only one form of apparatusembodying my invention, it is understood that various changes andmodifications may be made therein within the scope of the appendedclaims without departing from the spiritand scope of my invention.

Having thus described my invention, what I claim is: v I

1. In combination, a section of railway track, means for supplying codedtrackway energy" to the rails of said section,- two tubes eachcomprising two spaced electrodesand a grid in a medium which forms aconducting path between. said electrodes when and onlywhen'the'potential be tween the electrodes exceeds a value whichdependsupon the relative potential of the grid with respect to one of saidelectrodes, an output cir cuit for each of said two tubes including thetwo spaced electrodes of the associated tube, means for impressingacross the grid andsaid one electrode of one of said two tubes a biasingelectromotive force which normally renders that tube conducting, meansfor impressing across the grid and said one electrode of the other ofsaid two tubes a biasing electromotive force which normally renders thattube non-conducting, means receiving energy from the track rails forimpressing across the grid and said one electrode of each of saidtwotubes an electromotive force which opposes the biasing electromotiveforce normally impressed thereon to render said one tube non-conductingand said other tube conducting for the interval in which energy isreceived from the track rails, and railway traific controlling apparatuscontrolled by the output circuits of said two tubes.

2. In combination, a section of railway track, means for supplying codedtrackway energy to the rails of said section, two tubes each comprisingtwo spaced electrodes and a grid in a medium which forms a conductingpath between said electrodes when and only when the potential betweentheelectrodes exceeds a. value which depends upon the relative potentialof the grid with respect to one of said electrodes, a decodingtransformer, a source of alternating current, a circuit including saidtwo electrodes of one of said two tubes connected in series with saidsource for supplying from said source rectified current of a givenpolarity to said decoding transformer, a circuit including said twoelectrodes of the other of said two tubes connected in series with saidsource for supplying from said source rectified current of the otherpolarity to said decoding transformer, circuit means for impressingacross the grid and said one electrode of each of said two tubes abiasing electromotive force effective to render said one tube normallyconducting and said other tube normally non-conducting, means receivingenergy from the track rails for impressing across the grid and said oneelectrode of each of said two tubes an electrornotive force whichopposes said biasing electromotive force to render said one tubenon-conducting and said other tube conducting for the interval thatenergy is received from the track rails, and trafiic controllingapparatus controlled by energy supplied from said decoding transformer.

3. In combination with adjoining advance and rear subsections of railwaytrack, means for supplying coded trackway energyto the track rails ofsaid advance subsection, an electron tube comprising two spacedelectrodes and a control grid in a medium which forms a conducting pathbetween said electrodes when and only when the potential between theelectrodes exceeds a value which depends upon the relative potential ofthe control grid with respect to one of said electrodes, means forimpressing across the control grid and said one electrode of said tube abiasing electromotive force which normally renders said tubenon-conducting, means receiving energy from the track rails of saidadvance subsection for impressing across the control grid and said oneelectrode of said tube an electromotive force opposing saidbiasing'electromotive force whereby said tube is rendered conducting forthe interval in which energy is received from the track rails of saidadvance subsection, a source of energy, a saturation relay having amagnetizable core provided with impedance windings connected in serieswith said source of energy and also provided with a .control windingeffective when energized to supply a saturating flux to said corewhereby to vary the impedance of said impedance windings, meansincluding a source of current connected across the two electrodes ofsaid tube for energizing said control winding of said relay only whensaid tube is in its conducting condition, whereby there will be effecteda sharp decay in the saturating flux supplied to the relay core, andmeans for connecting the impedance windings of said relay across thetrack rails of said rear subsection whereby the track rails of said rearsubsection are supplied with energy from said source of energy ascontrolled by the supply of energy to the control winding of said relay.I

4. In combination with a section of railway track divided into anadvance and a rear subsection and having means for supplying codedtrackway energy to the rails of said advance subsection, an outputwinding mounted on a magnetizable core, a source of periodically varyingcurrent, means including said output winding for connecting said sourceto the rails of said rear subsection, a control winding also mounted onsaid core and effective when supplied with cur rent to control thetransfer of energy from said source tosaid rear subsection through saidoutput winding in accordance with the magnetic flux created in such coredue to current in said control winding, an electronic tube controlled bycoded trackway energy received from the rails of said advancesubsection, and means controlled by said electronic tube for supplyingcurrent to said control winding whereby the coded trackway energy ofsaid advance subsection causes undistorted code to be supplied to therails of said rear subsection due to the sharp cut-off in current passedby said tube.

5. In combination with a section of railway track divided into anadvance and a rear sub section and having means for supplying codedtrackway energy to the rails of said advance subsection, a saturablereactor having a main winding disposed on a magnetizable core, a sourceof alternating current, means for connecting said source to the rails ofsaid rear subsection through said main reactor winding, a controlwinding for said reactor disposed on said core and eifective to vary theimpedance of said main reactor winding by varying the magnetic flux setup in said core due to current in said control winding, an electronictube controlled by coded trackway energy received from the rails of saidadvance subsection, and means controlled by said electronic tube forsupplying current to said control winding whereby the coded trackwayenergy of said advance subsection causes undistorted code to be suppliedto the rails of said rear subsection due to the sharp cut-off in currentpassed by said tube.

BERNARD E. OHAGAN.

